Node.js doesn't have good place to call contextDestroyed.
We need to cleanup everything on our side to allow clients to not call
contextDestroyed method.

R=dgozman@chromium.org,eostroukhov@chromium.com

Bug: none
Change-Id: Ibe3f01fd18afbfa579e5db66ab6f174d5fad7c82
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/575519Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#46849}
Reviewed-on: https://chromium-review.googlesource.com/596549
Cr-Commit-Position: refs/heads/master@{#47060}